Consumer products, such as electronic devices (e.g., mobile phones, portable media players, personal digital assistants, computers, monitors, etc.), have been marked with information for commercial, regulatory, cosmetic or functional purposes. For example, it is common for electronic devices to be marked with serial numbers, model numbers, copyright information, alphanumerical characters, logos, operating instructions, decorative lines, patterns, and the like. Desirable attributes for a mark include the shape, color, optical density, and any other attribute that may affect the appearance of the mark.
Numerous processes can be used to produce a mark on a product or article depending on, for example, the nature of the article itself, the desired appearance of the mark, the desired durability of the mark, and the like. Marking processes have been developed that use lasers to produce visible marks on metallic articles, polymeric articles, and the like. A conventional marking process is understood to involve directing a beam of laser pulses to impinge upon the article at spot areas, and raster-scanning the beam within an area to be marked. Thus marks formed by conventional marking processes are generally composed of a series of successively-formed, and overlapping, scan lines that are each formed of a series of successively-formed, and overlapping, spot areas. Conventionally, the throughput of such marking processes has been increased simply by increasing the pulse repetition rate (e.g., such that a period between pulses is in a range from 500 ns to 1 μs) and scan speed (e.g., to maintain a desired bite size) while maintaining a constant pulse energy. However, the inventors have discovered that this throughput enhancing process only works up to a point, after which the rapid accumulation of successively-directed laser pulses on the article during the marking process actually creates undesirable defects (e.g., cracks, material warping, modified crystalline structures, pits, etc.) that can physically or chemically damage the article or undesirably change the visual appearance of the article. The inventors have further discovered that such rapid accumulation of successively-directed laser pulses onto the article can also degrade the appearance of the mark that is ultimately formed. Thus it would be desirable if a laser marking process existed that had a high throughput and avoided these and other problems associated with the rapid accumulation of successively-directed laser pulses onto the article.